1. Field of the Invention
The present invention relates to a semiconductor device, a wafer structure and a method for fabricating the semiconductor device and more specifically to the semiconductor device, the wafer structure and the method for fabricating the semiconductor device using compound semiconductors.
2. Description of the Photo-Resist Related Art
Conventionally, a WCSP (Wafer-Level Chip Size Packaging) technique is used in general in fabricating semiconductor devices to accommodate to semiconductor devices whose size and weight are reduced. The WCSP separates the semiconductor devices into individual chips by dicing the wafer after forming rewiring layers and passivation layers in a state of the wafer. In dicing the wafer, a trench whose width is wider than a dicing blade is formed along a scribing region that is a part to be cut and a bottom of the trench is cut by a dicer in an array direction as disclosed in Japanese Patent Application Laid-open No. Hei. 9-330891 for example. A silicon oxide film is used in general as a mask in forming the trench due to its easiness in forming the film and its cost.
In addition, semiconductor elements using various compound semiconductors such as III-V group semiconductors and II-VI group semiconductors are being developed lately because it has become possible to form various semiconductor elements and because it is required to operate and drive semiconductors more quickly at low voltage.
While the compound semiconductors described above are used to form semiconductor elements such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a HEMT (High Electron Mobility Transistor) and a SBD (Schottky Barrier Diode) for example, a metal film such as aluminum (Al) is normally used as an electrode material such as a gate electrode and others due to its low fabrication cost and its easiness of the fabrication process. However, because the metal film of this sort is soluble in etchant such as hydrofluoric acid used in etching a silicon oxide film used as a mask, the metal film causes problems that it complicates a fabrication process and limits a degree of freedom in selecting materials if the trench to be cut is formed in the scribing region after forming the various electrodes.
The prior art fabrication method is thus arranged to form the trench in the scribing region before forming the various electrodes from the reasons as described above. However, if the process (referred to as a microfabrication process hereinafter) that requires such a relatively fine fabrication process of forming the various electrodes is placed behind the process of forming the trench, there exists the trench whose width is larger than a thickness of the dicing blade or a diameter of a spot of a laser cutter for example at the time of the microfabrication process. This causes a problem that a photo-resist used in photolithography in the microfabrication process cannot be formed uniformly.